CN115260416A - High-temperature-resistant water-based drilling fluid nano-composite filtrate reducer and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of oil drilling fluid, in particular to a high-temperature-resistant water-based drilling fluid nano-composite fluid loss additive and a preparation method thereof, wherein the fluid loss additive comprises acrylamide, N-vinyl pyrrolidone, 2-acrylamide-2-methylpropanesulfonic acid, a cationic monomer and a nano-material carbon dot; the mass of the carbon dots of the nano material is 1.8 to 3 percent of the total mass of the monomers. The filtrate reducer and the preparation method thereof can effectively solve the problems of complex preparation process, high cost and easy hydrolysis of modified carbon point ester groups in the prior art.

Description

High-temperature-resistant water-based drilling fluid nano-composite filtrate reducer and preparation method thereof

Technical Field

The invention relates to the technical field of oil drilling fluid, in particular to a high-temperature-resistant water-based drilling fluid nano-composite filtrate reducer and a preparation method thereof.

Background

The level of drilling fluid technology is directly related to the quality, progress and cost of drilling construction. Particularly, in the drilling process of deep wells and ultra-deep wells, the severe environment of underground high temperature and high pressure can bring a plurality of complex and troublesome problems to the construction process. In order to ensure smooth high-temperature drilling, the drilling fluid has good temperature resistance, and can maintain that various rheological parameter indexes are not changed violently even in the environment that the downhole temperature exceeds 230 ℃. Meanwhile, under the complex environment of high temperature and high salt, the polymer treating agent in the wellbore drilling fluid can generate high-temperature damage effects such as high-temperature degradation, high-temperature crosslinking, high-temperature desorption, high-temperature dehydration and the like, so that the performance of the drilling fluid is poor or even worsened, the requirements of drilling engineering can not be met, the normal operation of drilling operation is seriously influenced, and the safety risk of the deep well drilling engineering is greatly increased. And the drilling fluid filtration loss is large, so that the water-sensitive stratum absorbs water and expands, the diameter is reduced, the drilling resistance is blocked, and the large-section reaming is realized; collapse of hard and brittle formations (shale, crushed dolomite, igneous rock) with microcrack development; the invasion of the filtrate can cause the clay mineral in the reservoir to expand, reduce the seepage channel, increase the resistance of oil gas flowing into the well, reduce the relative permeability of the oil gas and finally reduce the yield of the oil gas well.

Compared with the conventional reservoir, the unconventional compact reservoir has strong heterogeneity, small pores and throats, mainly nano-scale pore systems, locally developed micron-millimeter-scale pores, complex and various pore throat structures with different microscale, and the pore types are diverse, including intraparticle pores in organic matter, intraparticle pores in minerals, intergranular pores between minerals and organic matter or between mineral particles, and microcracks.

The filtrate reducer can be adsorbed on the surface of clay particles, ionizes a large number of negative charge groups, improves the zeta potential and the thickness of a hydrated film of the clay particles, avoids clay colloidal particles from coalescing, can be applied to the oil field drilling process, can effectively reduce the filtrate loss, and is a key material in a drilling fluid treating agent. The current research on polymer fluid loss additives mainly focuses on improving the temperature and salt resistance of the polymer fluid loss additives. Most of the conventional fluid loss agents are applied below 180 ℃, the performance of the fluid loss agent is obviously reduced when the bottom temperature is higher than 200 ℃, the dosage of the fluid loss agent is increased to meet the requirement, and the drilling cost is increased. The current drilling commonly used foreign imported filtrate reducer Driscal-D, dristemp has higher cost.

In the prior art, a chinese invention patent document with publication number CN101691485 and publication date 2010, 04 and 07 is proposed, and the technical scheme disclosed in the patent document is as follows: in the patent, the salt resistance of the zwitterionic polymer filtrate reducer is weaker, 2 percent of PAADS is aged in 4 percent sodium chloride salt water slurry at the high temperature of 200 ℃, FLAPI =65mL, and the filtrate loss is larger; in PAADS temperature resistance evaluation, 1.5 percent of the PAADS is aged at 200 ℃ for 16h, FLAPI =14.4mL, and the requirement of >220 ℃ is not met.

In summary, the filtrate reducer is an important component of the drilling fluid, and there are three main problems at present:

1. the temperature resistance is poor, but in the severe environment with high temperature of more than 230 ℃, the polymer fluid loss additive is easy to degrade, flocculate and desorb, the protective capability of clay particles is weakened, the rheological property, the fluid loss property, the stability and other properties of the drilling fluid are out of control, and the treatment agent fails to play the role.

2. Salt resistance is poor and drilling requirements cannot be met in certain formations.

3. Some filtrate reducers with better performance depend on imports and have high cost.

In the prior art, a chinese patent document with publication number CN113150754a and publication date 2021, 07/23 is proposed to solve the above-mentioned technical problems, and the technical scheme disclosed in the patent document is as follows: the invention provides a temperature-resistant and salt-resistant water-based drilling fluid filtrate reducer and a preparation method thereof, which are generated by copolymerizing raw materials containing acrylamide, N-vinyl pyrrolidone, 2-acrylamide-dimethyl propanesulfonic acid and a zwitterionic monomer under the action of an initiator.

In the actual use process, the following problems can occur in the technical scheme:

in the technical scheme, the raw materials for synthesizing the zwitterionic monomer are complex, the cost is high, the synthesis process is complex, the purification steps of the synthesized product are complex, the synthesized yield is low, and industrial production is difficult to carry out.

In the prior art, a chinese patent disclosure with publication number CN114702632a, published as 2022, year 07 and month 05 is also proposed to solve the above technical problems, and the technical solution disclosed in the patent document is as follows: a fluid loss additive for water-based drilling fluid is prepared by copolymerizing monomer and modified carbon dots under the action of initiator, wherein the monomer contains a temperature-resistant hydration group sulfonic group, a rigid group pyridyl group and an N, N-dimethyl amide group with better rigidity and temperature resistance.

In the actual use process, the following problems can occur in the technical scheme:

the modified carbon points are modified by a silane coupling agent KH570, and a rotary evaporator is adopted to remove a reaction solvent ethanol, so that the ethanol is possibly not completely treated to influence modification; and the ester group connected with the C = C double bond on the modified carbon point is greatly influenced by pH and is easy to hydrolyze, so that the function of the modified carbon point is influenced.

Disclosure of Invention

In order to solve the technical problems, the invention provides a high-temperature-resistant water-based drilling fluid nano-composite filtrate reducer and a preparation method thereof, which can effectively solve the problems of complex preparation process, high cost and easy hydrolysis of modified carbon dot ester groups in the prior art.

The invention is realized by adopting the following technical scheme:

the high-temperature-resistant water-based drilling fluid nano composite filtrate reducer comprises monomers, wherein the monomers comprise acrylamide, N-vinyl pyrrolidone and 2-acrylamido-2-methylpropanesulfonic acid, and is characterized in that: the nano-material carbon dots also comprise a cationic monomer; the mass of the nano material carbon dots is 1.8-3% of the total mass of the monomer;

the molecular structural formula of the cationic monomer is as follows:

the filtrate reducer is prepared by copolymerization of monomers and nano material carbon dots under the action of an initiator; the chemical structural formula of the fluid loss agent is as follows:

wherein n, m, x and y are natural numbers.

The preparation method of the cationic monomer comprises the following steps: triethylamine and 4-vinyl Bian Lv are adopted as reaction raw materials, tetrahydrofuran is adopted as a solvent, the reaction is heated to 50 ℃ in a water bath, and the reflux reaction is carried out for 12 hours; and then, carrying out suction filtration on the reacted mixture to obtain a solid sample, and drying the solid sample at 50 ℃ in vacuum to obtain the cationic monomer.

The mol ratio of the acrylamide to the 2-acrylamido-2-methylpropanesulfonic acid is 70 (12-20); the mol ratio of the acrylamide to the N-vinyl pyrrolidone is 35 (1-5); the molar ratio of the acrylamide to the cationic monomer is 30 (2-5).

The initiator is an ammonium persulfate and sodium bisulfite redox system; wherein the molar ratio of ammonium persulfate to sodium bisulfite is 1.

The mass ratio of the total mass of the four monomers and the carbon dots of the nano material to the mass of the ammonium persulfate is 100: 0.1-0.7.

A preparation method of a high-temperature-resistant water-based drilling fluid nano-composite filtrate reducer is characterized by comprising the following steps: the method comprises the following steps:

S ₁ dissolving 2-acrylamido-dimethylpropanesulfonic acid in water;

S ₂ to step S ₁ Adding NaOH into the prepared solution to adjust the pH value of the solution to 5-9, then adding acrylamide, N-vinyl pyrrolidone and a cationic monomer to dissolve the solution, stirring the solution with magnetons for 15min, then adding a nano material carbon dot, performing ultrasonic dispersion for 10min, and then introducing nitrogen for 20-30 min and heating the solution at the same time;

S ₃ to step S ₂ And adding an initiator into the treated solution, continuously introducing nitrogen, stirring and reacting for 4-9h, after the reaction is finished, extracting the product by using ethanol, shearing, granulating, drying and crushing to obtain the high-temperature-resistant water-based drilling fluid nano composite filtrate reducer.

The mass ratio of the total mass of the acrylamide, the 2-acrylamide-dimethyl propanesulfonic acid, the N-vinyl pyrrolidone and the cationic monomer to the water is 1 (3-6).

Said step S ₂ And after the temperature is raised, controlling the temperature to be 45-65 ℃.

Said step S ₃ Chinese traditional medicineThe particle size of the obtained filtrate reducer is 100-300 meshes.

Compared with the prior art, the invention has the beneficial effects that:

1. compared with the patent document with the publication number of CN113150754A, the cationic monomer synthesized by the invention has a simple structure and does not have a sulfonic acid group; the 2-acrylamide-dimethyl propane sulfonic acid monomer contains sulfonic acid groups, so that the cationic monomer does not need to introduce sulfonic acid groups; and sulfonic acid groups are not introduced, so that the synthesis steps of synthesizing the monomers are simpler, the cationic monomers can be obtained without purification, and the engineering practice is facilitated. Moreover, experiments prove that the cationic monomer does not introduce sulfonic acid groups, has a simpler structure, and has no influence on the performance of the synthesized polymer fluid loss additive.

Compared with the patent document with the publication number of CN114702632A, the carbon dots of the nano material are not modified, because the carbon dots of the nano material have functional groups such as hydroxyl groups, carboxyl groups and the like, the carbon dots of the nano material directly undergo a polymerization reaction with a monomer, are wrapped in a polymer chain through a series of hydrogen bond actions and physical acting forces, are compounded in a large number of polymer chain-shaped and net-shaped structures of the polymer filtrate reducer, can still keep the appearance and the action after experiencing a deep high-temperature environment, can continuously exert the temperature resistance of the polymer filtrate reducer, and assist to form a compact and tough thin mud cake when forming a filter cake, thereby exerting the performance of the filtrate reducer. The invention does not modify the carbon points of the nano material, uses the existing material, has wide raw material sources, and can avoid the defect that the ester group is hydrolyzed after the modification of the silane coupling agent and can not play the role of the silane coupling agent. Compared with the modified carbon dots, the fluid loss agent prepared by adopting the nano material carbon dot composite mode has the advantages of simpler preparation process, increased addition of the nano material carbon dots and increased temperature resistance and fluid loss reduction performance.

In addition, in the invention, the quality of the carbon dots of the nano material is greatly improved, the carbon dots have stronger wrapping effect with the polymer fluid loss additive, more hydrogen bonds are formed, and the space network structure formed by compounding is stronger, so that the apparent viscosity and the plastic viscosity of the drilling fluid can be improved, the capability of the polymer fluid loss additive for regulating and controlling the rheological property of the drilling fluid is improved, and meanwhile, the fluid loss of the drilling fluid is also reduced after the viscosity is increased.

The composite filtrate reducer is additionally provided with a cationic monomer and a nano material carbon dot, and because the cationic monomer contains a benzene ring and a quaternary ammonium cation, the benzene ring and the rigid structure of the nano material carbon dot together provide the temperature resistance for the composite filtrate reducer, and the benzene ring and the nano material carbon dot have a coordination effect; the quaternary ammonium cation and hydroxyl and carboxyl on the carbon points of the nano material generate an adsorption and wrapping effect, so that the carbon points of the nano material are inserted into the polymer chain links to play a role of the carbon points. From the aspect of performance, the two are adopted for free radical copolymerization, so that the temperature resistance of the synthesized composite polymer fluid loss additive is improved, and the water-based drilling fluid base slurry also keeps better rheological property and fluid loss reduction performance after being subjected to thermal roll aging at 240 ℃ for 16 hours.

2. For example, in the prior art, patent document No. CN113150754, the preparation of zwitterionic monomer in this document includes 2 steps, the first step reaction obtains an intermediate, the intermediate needs to be purified by column chromatography, the purification process is complicated, the target product can be obtained after the second step reaction, and the target product needs to be stored at 2-8 ℃, and the storage condition is strict. On the contrary, the preparation method of the cationic monomer adopted in the invention has simple reaction monomer and reaction process, the cationic monomer obtained after the reaction is insoluble in a reaction solvent, so the cationic monomer can be obtained by suction filtration, a pure reaction product can be obtained through nuclear magnetic analysis without purification, the storage temperature is normal temperature, the storage is convenient, and a foundation is provided for the synthesis of the subsequent fluid loss additive.

3. The invention also optimizes the proportion of the components, so that the additive is more suitable for the addition of the cationic monomer and the carbon dots of the nano material, the effect of the copolymerization of the carbon dots of the nano material and other monomers in a composite form is better, and the overall performance of the fluid loss additive is improved.

4. When the filtrate reducer is prepared, the pH value is adjusted in advance, the residual monomer and the nano-material carbon dots are added, and magneton stirring and ultrasonic dispersion are utilized, so that the nano-material carbon dots have good copolymerization effect with other monomers in a composite form.

5. The particle size of the filtrate reducer is 100-300 meshes, so that the filtrate reducer is easy to dissolve in the base slurry of the water-based drilling fluid to play a role.

Drawings

The invention will be described in further detail with reference to the following description taken in conjunction with the accompanying drawings and detailed description, in which:

FIG. 1 is a nuclear magnetic hydrogen spectrum of a cationic monomer prepared in the present invention;

FIG. 2 is a TEM image of a hydrothermally prepared carbon dot in the present invention;

FIG. 3 is an IR spectrum of a hydrothermal prepared carbon dot of the present invention;

fig. 4 is a dried morphology of the fluid loss agent prepared in example 3;

fig. 5 is a plot of API medium pressure fresh water and brine-based slurries at ambient temperature to which the fluid loss additives prepared in example 3 were added;

FIG. 6 is a graph comparing medium pressure API filter cake before and after aging of fresh water based slurries to which fluid loss additives of examples 3 and 4 were added;

FIG. 7 is a high temperature, high pressure filter cake of a fresh water based slurry containing the fluid loss additive of example 3;

figure 8 is a high temperature, high pressure filter cake of a fresh water based slurry containing the fluid loss additive of example 4;

figure 9 is a graph comparing medium pressure API press cake before and after aging of brine-based slurries to which fluid loss additives of examples 3 and 4 were added;

FIG. 10 is a plot of the high temperature high pressure filter cake and the medium pressure API filter cake before and after aging of the fresh water based slurry to which the fluid loss additive of example 4 was added;

FIG. 11 shows the high-temperature high-pressure filter cake and the medium-pressure API filter cake before and after aging of the fresh water-based slurry added with the common fluid loss additive A;

FIG. 12 shows the high-temperature high-pressure filter cake and the medium-pressure API filter cake before and after aging of the fresh water-based slurry added with the conventional fluid loss additive B;

FIG. 13 shows the high-temperature high-pressure filter cake and the medium-pressure API filter cake before and after aging of a fresh water-based slurry added with a conventional fluid loss additive C;

fig. 14 shows the medium pressure API cake and the high temperature high pressure cake before and after aging of the fresh water-based slurry to which conventional fluid loss additive D was added.

Detailed Description

Example 1

The nano-material carbon dots for preparing the fluid loss additive can be obtained by the following preparation method.

(1) The carbon dots can be synthesized by using a microwave reaction method by adopting urea and citric acid, and the synthesis method is referred to as Di Yuechen. Preparation and application of a fluorescent composite material based on the carbon dots [ D ]. University of China academy of sciences (Changchun optical precision machinery and physical research institute), 2020. The specific synthesis method comprises the following steps: weighing 3g of anhydrous citric acid and 6g of urea, pouring the anhydrous citric acid and 6g of urea into a 100mL beaker, adding 20mL of pure water, placing the beaker filled with the solution on a magnetic stirrer, stirring and dissolving the mixture, placing the beaker into a microwave oven, heating the beaker by microwaves for 5 minutes to obtain a black solid mixture, taking out the beaker, and adding 40mL of pure water to dissolve the solid to obtain a dark brown solution; then putting the solution into a centrifuge tube, placing the centrifuge tube on a centrifuge for centrifuging twice, wherein the centrifugation speed is 8000r/min, each time is 5min, retaining the solution, and removing solids; and finally, sequentially passing the centrifuged solution through 0.45 and 0.22 mu m water-based filter membranes to finally obtain a carbon dot solution, and finally performing freeze drying to obtain carbon dots.

(2) The carbon dots can also be prepared by a hydrothermal method: 1.15g of citric acid was weighed, dissolved in 20mL of deionized water, and sufficiently dissolved by sonication. The prepared solution is transferred into a 30mL hydrothermal reaction kettle containing a polytetrafluoroethylene lining and reacts for 4h at 200 ℃ in a muffle furnace. After the reaction is finished, naturally cooling the reaction system to room temperature, and removing the supernatant; and weighing 1.5g of sulfanilic acid, adding the sulfanilic acid into the supernatant, performing ultrasonic treatment to fully dissolve the sulfanilic acid, transferring the solution into a hydrothermal reaction kettle, and reacting for 5 hours at 135 ℃ in a muffle furnace. After the reaction is finished, naturally cooling the reaction system to room temperature again, removing the supernatant, sequentially passing through 0.45 and 0.22 mu m water-based filter membranes to finally obtain a carbon dot solution, and finally freeze-drying to obtain the carbon dots.

Referring to FIG. 2 of the specification, it can be seen from FIG. 2 that the particle size of the carbon dots is 1 to 20nm. Referring to FIG. 3 of the specification, it can be seen from FIG. 3 that the distance is 3409cm ^-1 And 3118cm ^-1 The stretching vibration absorption peaks correspond to the hydroxyl on the surface of the carbon point and the O-H of the carboxyl respectively; 2775cm ^-1 、2368cm ^-1 、777cm ^-1 、596cm ^-1 And 543cm ^-1 The stretching vibration absorption peak corresponds to C-H in the carbon points; 1720cm ^-1 And 1624cm ^-1 The stretching vibration absorption peak corresponds to C = O in the carbon point; 1400cm ^-1 And 1066cm ^-1 The absorption peaks of stretching vibration at (A) correspond to C-C and C-N in the carbon points. According to the infrared data of the carbon points, the carbon points have a plurality of hydroxyl groups and carboxyl groups, and the carbon points are mainly formed by connecting C-C and C-N, so that the carbon points can be mutually verified with the literature, and the successful synthesis of the carbon points is indicated.

Example 2

The cationic monomer for preparing the filtrate reducer is obtained by the following preparation method:

weighing 60mL of tetrahydrofuran, adding the tetrahydrofuran into a three-neck flask, adding 9.91g of triethylamine and 5.0g of 4-vinyl Bian Lv, stirring by using a magneton in a constant-temperature water bath kettle, removing oxygen by using a three-way device, heating reactants to 50 ℃, connecting a reflux device, and carrying out reflux reaction for 12 hours. And (3) carrying out suction filtration on the mixture after reaction, recovering to obtain a solid sample, and then drying the solid product in a vacuum oven at 50 ℃ and storing at 2-8 ℃. And (3) carrying out related nuclear magnetic hydrogen spectrum test on the product, and referring to the attached figure 1 of the specification. It can be seen that δ 7.50, δ 7.39 are the hydrogens on the benzene ring; δ 6.73, 5.85, 5.32 is hydrogen on the vinyl group; delta 4.28 and delta 3.12 are corresponding peaks of a plurality of methylene groups on the monomer; delta 1.29 is 3 methyl corresponding peaks, which proves the success of the cationic monomer synthesis.

Example 3

A high-temperature-resistant water-based drilling fluid nano-composite filtrate reducer and a preparation method thereof. The fluid loss additive comprises 40g of acrylamide, 1.78g of N-vinyl pyrrolidone, 20g of 2-acrylamido-2-methylpropanesulfonic acid, 13.662g of cationic monomer and 1.358g of nanomaterial carbon dots. Wherein the nanomaterial carbon dots are prepared by the hydrothermal method in example 1 above. The cationic monomer is prepared by the preparation method in the embodiment 2, and the molecular structural formula of the cationic monomer is as follows:

the chemical structural formula of the fluid loss agent is as follows:

wherein n, m, x and y are natural numbers.

The preparation method of the fluid loss agent comprises the following steps: 301.86g deionized water and 20g 2-acrylamido-2 methylpropanesulfonic acid were charged into a four-necked flask equipped with a stirrer, a reflux condenser, a thermometer, and a heating device; naOH is added to adjust the pH value to 5.0, then 40g of acrylamide, 1.78g N-vinyl pyrrolidone and 13.662g of cationic monomer are added to dissolve, magnetons are stirred for 15min, 1.358g of nano material carbon dots are added, ultrasonic dispersion is carried out for 10min, then nitrogen is introduced for 20-30 min, and the temperature is raised to 45 ℃ at the same time. Ammonium persulfate (0.259 g) and sodium bisulfite (0.118 g) were added and the nitrogen flow was continued for half an hour and then stopped. The reaction lasts for 4 hours, after 4 hours, the semisolid polymer is poured into an ethanol solution for purification, is sheared and granulated, the particle size of the filtrate reducer is 100-300 meshes, and is then put into a 65 ℃ drying oven for drying; drying and crushing to obtain yellow powder, and specifically referring to the attached figure 4 of the specification, the yellow powder is the nano composite fluid loss additive which is named as fluid loss additive 1.

Example 4

A high-temperature-resistant water-based drilling fluid nano-composite filtrate reducer and a preparation method thereof. The fluid loss additive comprises 30.01g of acrylamide, 6.7g N-vinyl pyrrolidone, 25g of 2-acrylamido-2-methyl propane sulfonic acid, 25.604g of cationic monomer and 2.62g of nanomaterial carbon dots. Wherein the nanomaterial carbon dots are prepared by the microwave method in example 1 above. Wherein the cationic monomer is prepared by the preparation method in the embodiment 2, and the molecular structural formula of the cationic monomer is as follows:

the chemical structural formula of the fluid loss agent is as follows:

in the formula, n, m, x and y are natural numbers.

The preparation method of the filtrate reducer comprises the following steps: 349.27g deionized water and 25g 2-acrylamido-2-methylpropanesulfonic acid were added to a four-necked flask equipped with a stirrer, a reflux condenser, a thermometer, and a heating device; naOH is added to adjust the pH value to 9.0, then 30.01g of acrylamide, 6.7g N-vinyl pyrrolidone and 25.604g of cationic monomer are added to dissolve, magnetons are stirred for 15min, 2.62g of nano material carbon dots are added, ultrasonic dispersion is carried out for 10min, then nitrogen is introduced for 20-30 min, and the temperature is increased to 65 ℃ at the same time. 0.2998g of ammonium persulfate was added, 0.1368g of sodium bisulfite was added, the nitrogen gas was continuously introduced, and the nitrogen gas introduction was stopped after half an hour. The reaction lasts for 8 hours, after 8 hours, the semisolid polymer is poured into ethanol solution for purification, and is cut into pieces for granulation, so that the particle size of the filtrate reducer is 100-300 meshes, and then the filtrate reducer is placed into a 65 ℃ oven for drying; drying and crushing to obtain yellow powder, namely the nano composite fluid loss agent, which is named as fluid loss agent 2.

Example 5

A high-temperature resistant water-based drilling fluid nano-composite filtrate reducer and a preparation method thereof. The fluid loss additive comprises 37.515g of acrylamide, 5.865g N-vinyl pyrrolidone, 25g of 2-acrylamido-2-methyl propane sulfonic acid, 25.506g of cationic monomer and 2.065g of nanomaterial carbon dots. Wherein the nanomaterial carbon dots are prepared by the microwave method described above in example 1. Wherein the cationic monomer is prepared by the preparation method in the embodiment 2, and the molecular structural formula of the cationic monomer is as follows:

the chemical structural formula of the fluid loss agent is as follows:

wherein n, m, x and y are natural numbers.

The preparation method of the filtrate reducer comprises the following steps: 375.54g deionized water and 25g 2-acrylamido-2-methylpropanesulfonic acid were added to a four-neck flask equipped with a stirrer, reflux condenser, thermometer, and heating device; naOH is added to adjust the pH value to 7.0, 37.515g acrylamide, 5.865g N-vinyl pyrrolidone and 25.506g cationic monomer are added to dissolve, magnetons are stirred for 15min, 2.065g nano material carbon dots are added, ultrasonic dispersion is carried out for 10min, then nitrogen is introduced for 20-30 min, and the temperature is raised to 55 ℃. Ammonium persulfate (0.322 g) and sodium bisulfite (0.147 g) were added, and the nitrogen addition was continued for half an hour and stopped. The reaction lasts for 5 hours, after 5 hours, the semisolid polymer is poured into ethanol solution for purification, and is cut into pieces for granulation, so that the particle size of the filtrate reducer is 100-300 meshes, and then the filtrate reducer is placed into a 65 ℃ oven for drying; drying and crushing to obtain yellow powder, namely the nano composite filtrate reducer which is named as filtrate reducer 3.

Performance test experiments were performed on the fluid loss additives prepared in examples 3, 4 and 5 as follows.

The related performance test method comprises the following steps:

(1) The preparation method of the drilling fluid base slurry comprises the following steps:

preparation of 4% bentonite slurry: tap water, 4.0 percent of bentonite (mass fraction) and 0.2 percent of soda ash (mass fraction) are stirred for 20min at a speed of 600r/min by using a low-speed stirrer in a slurry cup; then stirring for 10min at 12000r/min by using a high-speed stirrer, then standing and hydrating for 16-24h, and using the mixture for experiment after 16h of hydration.

And taking out the prehydrated bentonite slurry, placing the prehydrated bentonite slurry in a low-speed stirrer for stirring, adding the prepared fluid loss additive, stirring for 10min by using the low-speed stirrer, and stirring for 5min at a high speed to obtain the bentonite slurry for evaluation experiments.

15% saline slurry base slurry: stirring tap water, 4.0% of bentonite (mass fraction), 0.2% of soda (mass fraction) and 15% of sodium chloride (mass fraction) at a speed of 600r/min for 20min, then transferring to a high stirring cup, stirring at a speed of 12000r/min for 10min, and curing at room temperature for 16-24h to obtain saline water-based slurry.

(2) And (4) detecting the conventional performance.

The rheological property test and the normal-temperature medium-pressure filtration loss test of the drilling fluid are carried out according to the detection method of the national standard GB/T16783.1-2014. Detecting parameters: AV (apparent viscosity), PV (plastic viscosity), YP (dynamic shear), GEL (static shear), FL _API (Normal temperature medium pressure filtration loss) FL _HTHP (high temperature high pressure filtration loss).

(3) And testing the temperature resistance of the drilling fluid.

The temperature resistance test of the drilling fluid comprises a high-temperature high-pressure filtration loss test and a high-temperature heat rolling aging test. And (3) carrying out drilling fluid performance detection according to a detection method of national standard GB/T16783.1-2014.

The high-temperature thermal rolling aging test process comprises the following steps: taking out after thermal rolling at 240 ℃/16h aging, and measuring the related performance of the drilling fluid at 30 ℃ after the drilling fluid is stirred at a high speed for 10 min.

Fluid loss additive rheology and filtration loss at normal temperature

Taking two parts of pre-hydrated fresh water-based slurry and two parts of pre-hydrated brine-based slurry, adding 1wt% of fluid loss additive 1 (product of example 3) into the fresh water-based slurry and the brine-based slurry under the condition of continuous stirring, and uniformly stirring at a high speed, and marking as fluid loss additive 1 fresh water-based slurry and fluid loss additive 1 brine-based slurry. The results of the rheological test and the fluid loss test were performed on the fresh water-based slurry, the brine-based slurry, the fluid loss additive 1 fresh water-based slurry, and the fluid loss additive 1 brine-based slurry, respectively, and are shown in table 1. In Table 1, AV is the apparent viscosity, PV is the plastic viscosity, YP means the dynamic shear force, FL _API The normal temperature and pressure drilling fluid filtration loss is referred to.

TABLE 1 testing instrument for normal temp. flowing denaturation and filtration loss of filtrate reducer

Experimental pulp	AV(mPa . S)	PV(mPa . S)	YP(Pa)	FL API (mL)
					Fresh water base pulp	8	6	2	45.6
Saline water-based slurry	4	3	1	71.8
					Filtrate reducer 1 fresh water-based slurry	50	27	23	6.5
Filtrate reducer 1 saline water-based slurry	36	26	10	11.6

As can be seen from Table 1, the filtrate reducer of the present invention has good filtrate reducing performance in a small amount, and the filter cake in the API formed by adding the filtrate reducer has a smooth, thin and compact surface, which is referred to in the attached figure 5 of the specification.

(II) fluid loss additive high temperature rheology and fluid loss

Three portions of prehydrated fresh water-based slurry are taken, one portion is taken as a blank sample, no filtrate reducer is added, 1wt% of the filtrate reducer 1 (prepared in example 3), the filtrate reducer 2 (prepared in example 4) and the filtrate reducer 3 (prepared in example 5) are respectively added into the other two portions of fresh water-based slurry under the condition of continuous stirring, and the mixture is uniformly stirred at a high speed and is marked as the filtrate reducer 1 fresh water-based slurry, the filtrate reducer 2 fresh water-based slurry and the filtrate reducer 3 fresh water-based slurry. And (3) respectively carrying out 240 ℃/16h hot rolling aging experiments on the fresh water base slurry blank sample, the filtrate reducer 1 fresh water base slurry, the filtrate reducer 2 fresh water base slurry and the filtrate reducer 3 fresh water base slurry, taking out after the experiments, and carrying out rheological property test and filtration loss test, wherein the results are shown in table 2.

TABLE 2 high-temp. flowability and filtration loss test table for filtrate reducer

As can be seen from Table 2, the nanocomposite fluid loss additive of the invention has good fluid loss performance after fresh water-based slurry and 240 ℃ hot roll aging, and after aging for 16 hours at 240 ℃, the settling performance is stable, the rheological property and the fluid loss performance are good, which indicates that the nanocomposite fluid loss additive can form a strong space grid structure on the basis of forming a compact hydration film and improving the electronegativity of soil particles, so as to improve the coalescence stability of the soil particles, and can also maintain a good space structure after high temperature aging, thereby achieving the effect of reducing the fluid loss. The high-temperature and high-pressure filter cake formed after aging has a smooth and compact surface, and specifically refers to the attached figures 6-8 of the specification.

(III) high-temperature high-salt rheology and filtration loss of filtrate reducer

Three portions of prehydrated brine-based slurry were taken, one portion was used as a blank, no fluid loss additive was added, and 1wt% of fluid loss additive 1 (prepared in example 3), fluid loss additive 2 (prepared in example 4) and fluid loss additive 3 (prepared in example 5) were added to the other two portions of brine-based slurry under continuous stirring and stirred at high speed uniformly, and the slurry was designated as fluid loss additive 1 brine-based slurry, fluid loss additive 2 brine-based slurry, fluid loss additive 3 brine-based slurry. And (3) respectively carrying out a hot rolling aging experiment at 240 ℃/16h on the brine base slurry blank sample, the filtrate reducer 1 brine base slurry, the filtrate reducer 2 brine base slurry and the filtrate reducer 3 brine base slurry, taking out after the experiment, and carrying out a rheological property test and a filtrate loss test, wherein the results are shown in table 3 and the specification and figure 9.

TABLE 3 rheology and filtration loss test table under high temperature and high salt conditions for fluid loss additive

As can be seen from Table 3 and the accompanying drawing of the specification of figure 9, the fluid loss additive of the invention has good rheological property and fluid loss reduction property after being subjected to hot roll aging for 16h at 240 ℃ in saline base slurry, which indicates that the fluid loss additive has good temperature resistance and salt resistance.

(IV) comparing the performance with the performance of the common filtrate reducer at home and abroad

Taking 5 parts of fresh water-based slurry, respectively adding 1wt% of the filtrate reducer 2 prepared in the example 4 and four domestic and foreign common filtrate reducers (A, B, C, D) into the pre-hydrated fresh water-based slurry under the condition of continuously stirring, wherein A, B is an acrylamide polymer filtrate reducer, C is a nitrile silicon polymer filtrate reducer, D is a sulfonated polymer filtrate reducer, and uniformly stirring at high speed. And (3) respectively carrying out 240 ℃ hot rolling aging experiments on the five kinds of fresh water base pulp, and respectively testing the rheological property and the filtration loss after aging. The results are shown in Table 4.

Table 4 fluid loss additives of the present invention and the prior art comparison of conventional fluid loss additives

As shown in Table 4, the temperature-resistant and salt-resistant nano composite fluid loss additive prepared by the invention is obviously superior to an imported fluid loss additive after aging compared with other 4 common fluid loss additives at home and abroad, has good temperature resistance and good performance, and can keep better rheological property. Reference is made to the attached drawings 10-14 in the specification, which are respectively real graphs of medium-pressure API filter cakes and high-temperature high-pressure filter cakes before and after the ageing of experimental slurry.

In a word, the invention adopts a self-made novel cationic monomer, simultaneously introduces rigid nano material carbon dots, and adopts a water solution free radical polymerization mode together with common monomers of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid and N-vinyl pyrrolidone to prepare the novel high temperature resistant water-based drilling fluid nano composite filtrate reducer. The cationic monomer contains a rigid group benzene ring and a quaternary ammonium cationic group, so that the temperature resistance and salt resistance of the synthetic polymer can be improved; the carbon dots are inorganic nano materials, the particle size of nano particles is small, the specific surface area is large, surface force, van der waals force and molecular force occupy dominant positions, interaction among nano particles or between the nano particles and a medium becomes more severe, and unique characteristics are obtained. The carbon dots are used as rigid plugging materials, can effectively plug nanometer-sized gaps, and prevent drilling fluid loss and instability of a well wall. Meanwhile, the nano particles can enhance the structure and temperature resistance of the clay and improve the performance of the polymer and the performance of the drilling fluid.

In summary, after reading the present disclosure, those skilled in the art can make various other corresponding changes without creative efforts according to the technical solutions and technical concepts of the present disclosure, which all belong to the protection scope of the present disclosure.

Claims (9)

1. The high-temperature-resistant water-based drilling fluid nano composite filtrate reducer comprises monomers, wherein the monomers comprise acrylamide, N-vinyl pyrrolidone and 2-acrylamido-2-methylpropanesulfonic acid, and is characterized in that: the nano-material carbon dots also comprise a cationic monomer; the mass of the nano material carbon dots is 1.8-3% of the total mass of the monomer; the molecular structural formula of the cationic monomer is as follows:

the filtrate reducer is prepared by copolymerization reaction of monomers and nano material carbon dots under the action of an initiator; the chemical structural formula of the fluid loss agent is as follows:

in the formula, n, m, x and y are natural numbers.

2. The high temperature resistant water-based drilling fluid nanocomposite fluid loss additive according to claim 1, wherein: the preparation method of the cationic monomer comprises the following steps: triethylamine and 4-vinyl Bian Lv are adopted as reaction raw materials, tetrahydrofuran is adopted as a solvent, the reaction is heated to 50 ℃ in a water bath, and the reflux reaction is carried out for 12 hours; and then, carrying out suction filtration on the reacted mixture to obtain a solid sample, and drying the solid sample at 50 ℃ in vacuum to obtain the cationic monomer.

3. The high temperature resistant water-based drilling fluid nanocomposite fluid loss additive according to claim 2, wherein: the mol ratio of the acrylamide to the 2-acrylamide-2-methylpropanesulfonic acid is 70 (12-20); the mol ratio of the acrylamide to the N-vinyl pyrrolidone is 35 (1-5); the molar ratio of the acrylamide to the cationic monomer is 30 (2-5).

4. The high temperature resistant water-based drilling fluid nanocomposite fluid loss additive according to claim 2, wherein: the initiator is an ammonium persulfate and sodium bisulfite redox system; wherein the molar ratio of ammonium persulfate to sodium bisulfite is 1.

5. The high temperature resistant water-based drilling fluid nanocomposite fluid loss additive according to claim 4, wherein: the mass ratio of the total mass of the four monomers and the carbon dots of the nano material to the mass of the ammonium persulfate is 100: 0.1-0.7.

6. A preparation method of a high-temperature-resistant water-based drilling fluid nano-composite filtrate reducer is characterized by comprising the following steps: the method comprises the following steps:

S ₁ dissolving 2-acrylamide-dimethyl propanesulfonic acid in water;

S ₂ to step S ₁ NaOH is added into the prepared solution to adjust the pH value to 5-9, then acrylamide, N-vinyl pyrrolidone and cationic monomer are added to dissolve, stirring the magnetons for 15min, adding the carbon dots of the nano material, performing ultrasonic dispersion for 10min, and then introducing nitrogen for 20-30 min while heating;

S ₃ to step S ₂ And adding an initiator into the treated solution, continuously introducing nitrogen, stirring and reacting for 4-9 hours, after the reaction is finished, extracting the product by using ethanol, shearing, granulating, drying and crushing to obtain the high-temperature-resistant water-based drilling fluid nano composite filtrate reducer.

7. The preparation method of the high temperature resistant water-based drilling fluid nanocomposite fluid loss additive according to claim 6, wherein the preparation method comprises the following steps: the mass ratio of the total mass of the acrylamide, the 2-acrylamide-dimethyl propanesulfonic acid, the N-vinyl pyrrolidone and the cationic monomer to the mass of the water is 1 (3-6).

8. The preparation method of the high temperature resistant water-based drilling fluid nanocomposite fluid loss additive according to claim 6, wherein the preparation method comprises the following steps: said step S ₂ After the temperature is raisedThe temperature is controlled to be 45-65 ℃.

9. The preparation method of the high temperature resistant water-based drilling fluid nanocomposite fluid loss additive according to claim 6, wherein the preparation method comprises the following steps: said step S ₃ The particle size of the filtrate reducer prepared in the step (a) is 100-300 meshes.

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